I just got my summer holiday. And my goal is that my computer shal work the rest of the holiday. And a computer is like a ticking bomb. Eventually it will crash for a weird reason. So I need all the help I can receive to stop that from happen. I know a friend and his new computer stopped working cause it was an old mother card in it. Just spam me with advises to make this computer work this whole summer and possibly for a long time without crashing.

Hmm...well this is a very special case,i have like a 11th year old pc and it goes like the queen of slugs lol.
I can't guarantee you that these methods might make your pc faster,nor can resist a much more period of time,but here are my advices:
-Do not install thousand of programs on your pc and uninstall the programs wich you don't use at all.(It is said that they might bring applications that work in background and slows your machine).
-Clear out your temporary files from your system.A good way of making it faster is by installing Ccleaner,a free but very useful program.
-Try to use some registry fixers.(again Ccleaner has this feature too)
-Close some startup applications wich has little importance.(Ccleaner comes with this feature too,you can also use start--->run and type msconfig.)
-Try stopping some services that again,you don't need them,such as the xerox service if you don't have one(to access the program that handles services,click on start---->run and type services.msc,a video wich may help you is this)
-Try to format your pc from three to three months(or much more faster periods).I had a case where i haven't formated my pc for one year and it had 1-2 framerates per second when i was opening a program(and even runing them),this weird issue also happened on small programs(such as windows media player,browsers,etc...)
-Try updating your motherboard,sound and video drivers.They might have released versions that fixes some issues that happened on earlier versions and sometimes they might also improve your pc's performance.
-Get a good antivirus that has real-time protection and wich is very trusted (such as nod32) for your safety against viruses while browsing and opening/running programs.

Johannez691 wrote:I don't care about small viruses really. I just don't want the computer to suddenly shut down and never works to start again.

If you start having blue screens then the only remedy for it is by formatting your pc.
Also try to find out if your newly installed programs may affect your pc and uninstall them,and try to do those steps i said earlier about fixing the registry and clearing the temporary files.

It it just goes dark and power off while you're using it = it's probably overheating, install SpeedFan and check your CPU temperature : http://en.wikipedia.org/wiki/Speedfan
Above 80 C it's not good but it can happen, check it regularly.